Implantable medical devices (IMDs) such as pacemakers and implantable cardioverter defibrillators are utilized in monitoring and regulating various conditions within the body. An implantable cardioverter defibrillator, for example, may be utilized in cardiac rhythm management applications to monitor the rate and rhythm of the heart and for delivering various therapies such as cardiac pacing, cardiac defibrillation, and/or cardiac therapy. In some cases, the IMD can be configured to sense various physiological parameters occurring within the body to determine the occurrence of any abnormalities in the operation of the patient's heart. Based on these sensed parameters, the IMD may then deliver an appropriate treatment to the patient.
Communication with IMDs is sometimes accomplished via a wireless telemetry link between an external device and the IMD, or between the IMD and another device located within the body. In some cases, ultrasonic transducers can be used to establish an acoustic link with the IMD, allowing data, operational status, and other information to be wirelessly transmitted through the body via an acoustic signal. Establishing and maintaining an acoustic link between the IMD and the communicating device is often difficult, however, based on the acoustic path between the IMD and the communicating device. In some cases, for example, the acoustic link can be compromised by the presence of body organs, vessels, airways, and other anatomical structures within the body. Factors that can affect the performance of the acoustic link can include the implant location of the IMD within the body, the orientation of the IMD within the body, the presence of physiological noise (e.g., heart sounds, vibration, etc.) within the body, and the presence of body tissue interfaces or other areas where there is an abrupt change in acoustic impedance that can cause reflections and absorption of the acoustic signal.